Academic Commons Search Resultshttp://academiccommons.columbia.edu/catalog.rss?f%5Bpub_date_facet%5D%5B%5D=2012&f%5Bsubject_facet%5D%5B%5D=Mineralogy&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usGlobal variations in H2O/Ce: 1. Slab surface temperatures beneath volcanic arcshttp://academiccommons.columbia.edu/catalog/ac:145780
Cooper, Lauren B.; Ruscitto, Daniel M.; Plank, Terry A.; Wallace, Paul J.; Syracuse, Ellen M.; Manning, Craig E.Wed, 04 Apr 2012 00:00:00 +0000We have calculated slab fluid temperatures for 51 volcanoes in 10 subduction zones using the newly developed H2O/Ce thermometer. The slab fluid compositions were calculated from arc eruptives, using melt inclusion-based H2O contents, and were corrected for background mantle contributions. The temperatures, adjusted to h, the vertical depth to the slab beneath the volcanic arc, range from ~730 to 900°C and agree well (within 30°C on average for each arc) with sub-arc slab surface temperatures predicted by recent thermal models. The coherence between slab model and surface observation implies predominantly vertical transport of fluids within the mantle wedge. Slab surface temperatures are well reconciled with the thermal parameter (the product of slab age and vertical descent rate) and h. Arcs with shallow h (~80 to 100 km) yield a larger range in slab surface temperature (up to ~200°C between volcanoes) and more variable magma compositions than arcs with greater h (~120 to 180 km). This diversity is consistent with coupling of the subducting slab and mantle wedge, and subsequent rapid slab heating, at ~80 km. Slab surface temperatures at or warmer than the H2O-saturated solidus suggest that melting at the slab surface is common beneath volcanic arcs. Our results imply that hydrous melts or solute-rich supercritical fluids, and not H2O-rich aqueous fluids, are thus the agents of mass transport to the mantle wedge.Geochemistry, Mineralogy, Petrologytap3Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesThermochemical evolution of the sub-arc mantle due to back-arc spreadinghttp://academiccommons.columbia.edu/catalog/ac:145795
Hall, Paul S.; Cooper, Lauren B.; Plank, Terry A.Wed, 04 Apr 2012 00:00:00 +0000We present the results of a series of numerical geodynamic experiments designed to characterize the thermal and compositional evolution of the sub-arc mantle in response to spreading in the back-arc. We find large changes in both the temperature and composition of the sub-arc mantle with time as the BASC migrates away from the arc. In particular, the sub-arc mantle becomes increasingly more depleted with time following the onset of spreading, as mantle that has experienced decompression melting and melt extraction beneath the BASC is gradually drawn beneath the arc plate by slab-induced corner flow. The rate at which this depletion increases during the ~2 Myr immediately following the onset of spreading is controlled by the spreading rate at the BASC, with faster spreading leading to a more rapid increase in depletion. Following this initial period, depletion within the sub-arc mantle continues to increase at a somewhat slower pace. During this phase, the rate at which depletion increases is chiefly dictated by the subduction rate, with faster subduction leading to a more rapid increase in depletion beneath the arc. Depletion within the sub-arc mantle is also found to increase with increasing mantle potential temperature, decreasing age of the overriding plate, and decreasing distance between the initial location of the BASC and the arc. Predicted changes in the depletion of the sub-arc mantle with time are shown to be consistent with observations of systematic along-strike geochemical variations within a portion of the Tonga Arc adjacent to the Eastern Lau Spreading Center.Geophysics, Mineralogy, Petrology, Plate tectonicstap3Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticles